The need for being able to distinguish valid signatures from those which have been forged has been well established in the fields of business and banking for quite some time. Costly experience has taught that even a careful study of an individual's signature by a merchant or a banker is not an adequate safeguard since a skilled forger can often fool anyone who is not a handwriting expert. The problem of discerning between a forged signature and a valid signature is a problem which many have attempted to solve in the prior art.
Many of the more modern attempts have recognized that an individual's signature has associated therewith several distinct characteristics which can be detected by some means or another and converted into electrical signals which can be automatically processed and compared with the representation of an authentic signature for determination as to whether or not the signature currently being investigated is authentic or is a forgery.
One of the characteristics of an individual's signature which has been the focus of considerable attention is the characteristic pressure which is produced when an individual signs his signature. While this type of characteristic is not discernable to one who studies the signature on a piece of paper, or document, it can be detected and studied by other means. It has been found that the pressure variations produced when an individual signs his signature are characteristic of that individual's signature and can be used with an acceptable degree of accuracy for signature identification or verification purposes.
Most of the pressure transducing systems heretofore used in signature identification or verification systems have employed strain gages or similar transducing elements which produce a relatively weak electrical signal. Prior systems therefore have required substantial amplification before the relatively weak D.C. signal which was representative of the pressure variations produced when an individual writes his signature could be processed for signature identification purposes. The fact that these systems require the amplification of a relatively weak signal often resulted in an invalid comparison since the relatively weak signal could be lost in background noise and the like, and since the amplifiers generally used were subject to severe D.C. drift problems which often cause errors in the signal to be processed.